[MIPS] Add seccomp bpf support

sandbox/linux/seccomp-bpf/linux_seccomp.h

Index: sandbox/linux/seccomp-bpf/linux_seccomp.h
diff --git a/sandbox/linux/seccomp-bpf/linux_seccomp.h b/sandbox/linux/seccomp-bpf/linux_seccomp.h
index 0de0259da39ecdb745e5923b9a6ff3961c13be00..558014d9a18b18113c77c401036a72abfa0d78cf 100644
--- a/sandbox/linux/seccomp-bpf/linux_seccomp.h
+++ b/sandbox/linux/seccomp-bpf/linux_seccomp.h
@@ -26,6 +26,9 @@
 #ifndef EM_X86_64
 #define EM_X86_64 62
 #endif
+#ifndef EM_MIPS
+#define EM_MIPS   8
+#endif
 
 #ifndef __AUDIT_ARCH_64BIT
 #define __AUDIT_ARCH_64BIT 0x80000000
@@ -42,6 +45,9 @@
 #ifndef AUDIT_ARCH_X86_64
 #define AUDIT_ARCH_X86_64 (EM_X86_64|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
 #endif
+#ifndef AUDIT_ARCH_MIPSEL
+#define AUDIT_ARCH_MIPSEL    (EM_MIPS|__AUDIT_ARCH_LE)
+#endif
 
 // For prctl.h
 #ifndef PR_SET_SECCOMP
@@ -189,6 +195,42 @@
 #define SECCOMP_ARG_LSB_IDX(nr) (offsetof(struct arch_seccomp_data, args) +   \
                                  8*(nr) + 0)
 
+#elif defined(__mips__) && (_MIPS_SIM == _MIPS_SIM_ABI32)
+#define MIN_SYSCALL         __NR_O32_Linux
+#define MAX_PUBLIC_SYSCALL  (MIN_SYSCALL + __NR_Linux_syscalls)
+#define MAX_SYSCALL         MAX_PUBLIC_SYSCALL
+#define SECCOMP_ARCH        AUDIT_ARCH_MIPSEL
+
+// MIPS sigcontext_t is different from i386/x86_64 and ARM.
+// See </arch/mips/include/uapi/asm/sigcontext.h> in the Linux kernel.
+#define SECCOMP_REG(_ctx, _reg) ((_ctx)->uc_mcontext.gregs[_reg])
+// Based on MIPS o32 ABI syscall convention.
+// On MIPS, when indirect syscall is being made (syscall(__NR_foo)),
+// real identificator (__NR_foo) is not in v0, but in a0
+#define SECCOMP_RESULT(_ctx)    SECCOMP_REG(_ctx, 2)
+#define SECCOMP_SYSCALL(_ctx)   SECCOMP_REG(_ctx, 2)
+#define SECCOMP_IP(_ctx)        (_ctx)->uc_mcontext.pc
+#define SECCOMP_PARM1(_ctx)     SECCOMP_REG(_ctx, 4)
+#define SECCOMP_PARM2(_ctx)     SECCOMP_REG(_ctx, 5)
+#define SECCOMP_PARM3(_ctx)     SECCOMP_REG(_ctx, 6)
+#define SECCOMP_PARM4(_ctx)     SECCOMP_REG(_ctx, 7)
+// Only the first 4 arguments of syscall are in registers.
+// The rest are on the stack.
+#define SECCOMP_PARM5(_ctx)     (long int)(*((intptr_t*)SECCOMP_REG(_ctx,     \
+                                                                    29) + 4))
+#define SECCOMP_PARM6(_ctx)     (long int)(*((intptr_t*)SECCOMP_REG(_ctx,     \
+                                                                    29) + 5))
+#define SECCOMP_NR_IDX          (offsetof(struct arch_seccomp_data, nr))
+#define SECCOMP_ARCH_IDX        (offsetof(struct arch_seccomp_data, arch))
+#define SECCOMP_IP_MSB_IDX      (offsetof(struct arch_seccomp_data,           \
+                                          instruction_pointer) + 4)
+#define SECCOMP_IP_LSB_IDX      (offsetof(struct arch_seccomp_data,           \
+                                          instruction_pointer) + 0)
+#define SECCOMP_ARG_MSB_IDX(nr) (offsetof(struct arch_seccomp_data, args) +   \
+                                 8*(nr) + 4)
+#define SECCOMP_ARG_LSB_IDX(nr) (offsetof(struct arch_seccomp_data, args) +   \
+                                 8*(nr) + 0)
+
 #else
 #error Unsupported target platform